The invention relates to a brake lining and lined brake shoe for brake drums, in particular for brake drums of vehicles. The brake lining of the invention has advantageous heat conductivity properties due to its inner structural design and, accordingly, a longer useful life. Use of the present invention can result in avoidance of brake squeal and noises.
Aspects of ecology necessitate reduction of braking noises of vehicles, in particular elimination of brake squeal. At the same time, we are confronted with the problem of the insufficient useful life of brake linings. In particular, for heavy vehicles the main problem lies in that in comparison to the other structural elements the useful life of the brake linings is three times shorter. The linings are quickly worn and exchange is costly. Simultaneously, due to the disadvantageous heat conductivity of the brake linings, operational conditions of the connected structural elements, mainly of the brake drum, are negatively influenced, resulting in frequent repairs and exchange.
Known solutions have been either trifly effective or required structural modifications which could be realized only by the way of new solutions.
Known solutions and proposals, respectively, have attempted to reduce the phenomenon of brake squeal along two lines. In one approach, brake drums are designed so as not tending to vibration. The tendency toward vibration is reduced by rings or coils with a high inner damping pressed onto the outer surface of the brake drum. Or, linings exerting a damping effect are arranged in the channel formed in the flanged of the brake drum. The other approach has involved attempting to reduce brake squeal by an expedient formation of the brake shoe and the brake lining.
According to a known solution, brake linings of different hardness or made of different materials are used on the same brake or shoe, respectively or on the individual brake shoes within the same brake construction.
A brake lining is also known, which has different moduli of elasticity along the generatrix of the friction surface. That is, the extent of deformation is different under the influence of compressive force, since along the generatrix the thickness of the brake lining is different or the thickness is constant and inserts with a modulus of elasticity differing from the modulus of elasticity of the brake lining are embedded. These solutions require a more costly technological process, which is different from the presently used production technology of brake linings. Accordingly, their use with vehicles cannot be considered as economical.
Taking these circumstances into consideration, the object of our invention is to eliminate brake squeal occurring in the drum brakes of heavy vehicles without changing the shape and size of the brake lining and to increase possibly the very short useful life of the presently used brake linings.
It has been attempted to solve the aforementioned problem by the proper formation of the inner structure of the brake lining and in such a manner that the brake lining could be produced by applying the presently used technological methods or methods approximating said methods, simultaneously with low costs of production.
The technological cost-level of the production of brake linings is considerably influenced by the method of positioning of the reinforcing fibers or the fabric itself. In general, the reinforcing fibers with a relatively short fiberlength used to be admixed--in an irregular orientation--with the mass from which brake linings are produced, either individually in an arched finished form or in a band, by pressing, baking or rolling. Although irregular orientation of the fibers cannot be considered as advantageous, it represents the most simple technology. Brake linings with regular fiber orientation were also proposed. Decades ago it was recognized that in the course of wear of the brake lining, fibers which get their full length onto the frictioning surface are torn out from the lining in a short time, so that their reinforcing and heat conducting roles cannot be fulfilled.
In order to avoid this phenomenon it was proposed to prearrange and gather up the reinforcing fibers in such a manner that after having filled the space in between with the lining-mass, the fibers or at least the majority thereof lie perpendicularly to the frictional surface of the finished brake-lining. Fiber orientation of this character can be achieved with a fabric lining too, if the fibers lying normal to the frictional surface are stronger, and thicker than the cross fibers holding the normal fibers.
In another known solution, the web is arranged essentially parallel to the frictional surface, and the fibers are intercrossed at an acute angle. In this case, fibers are not torn out in longer pieces when they get onto the frictional surface. Fibers of different materials, mixed with each other or forming a web function differently in the material of the brake lining. With respect to temperature, asbestos fibers reduce the decrease in mechanical strength and admixed metal fibers also increase mechanical strength and perform the function of heat conductor within the brake linings. Earlier, mechanical strength had been increased by different inserts, e.g., by inserting a perforated sheet which was arranged parallel with the frictional surface.
In spite of these solutions aimed at the elimination of brake squeal or at a defined lining or fiber orientation brake squeal could not be eliminated with heavy vehicles.